This application claims the priority of German application 196 54 368.1, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a heat transfer device, particularly an exhaust gas heat transfer device, having a tube bundle consisting of rectangular tubes used for guiding the gas and having a jacket which surrounds the tube bundle, which is used for guiding a liquid coolant and which is provided with a coolant inlet and a coolant outlet.
A heat transfer device of the initially mentioned type is the object of commonly assigned German Patent Application P 195 40 683.4 and counterpart U.S. patent application Ser. No. 08/743,002, the disclosure of which is expressly incorporated by reference herein.
It is an object of the invention to develop a heat transfer device of the initially mentioned type such that the rectangular tubes and optionally also the jacket can be implemented with small wall thicknesses while the stability is nevertheless sufficient even if the gaseous medium and/or the liquid coolant are supplied under a certain pressure.
This and other objects have been achieved in that the rectangular tubes are provided with outwardly directed projections which determine the distance of adjacent rectangular tubes with respect to one another and with respect to the interior wall of the jacket.
This and other objects have also been achieved by providing an exhaust gas heat transfer device, comprising: a tube bundle including rectangular tubes used for guiding a gas; and a jacket surrounding the tube bundle, said jacket being used for guiding a liquid coolant and being provided with a coolant inlet and a coolant outlet, said rectangular tubes being provided with outwardly directed projections which determine a distance between adjacent of rectangular tubes with respect to one another and with respect to an interior wall of the jacket.
This and other objects have also been achieved by providing an exhaust gas heat transfer device, comprising: a tubular jacket defining a gas flow entrance and a gas flow exit in a flow direction; a plurality of tubes arranged inside said tubular jacket extending longitudinally in said flow direction, each said tube having a rectangular cross-section defined by an upper side, a lower side, and a pair of lateral sides, an interior of said tubes being communicated with said gas flow entrance and said gas flow exit, a plurality of projections projecting externally from at least one of said upper side and said lower side, said projections engaging an adjacent of said tubes such that spaces are defined between said adjacent tubes, said spaces being sealed off from said gas flow entrance and said gas flow exit.
According to the invention, the rectangular tubes support each other during the assembly to form a bundle. The exterior rectangular tubes of the tube bundle are supported on the jacket. With this construction, rectangular tubes with a small wall thickness can be used, and nevertheless a high resistance to pressure is achieved. In addition, the projections influence the flow of the liquid coolant so that the heat transfer is improved. Since a continuous exchange of the liquid coolant takes place, an O.sub.2 -diffusion is prevented which could cause a crevice corrosion.
As a further development of the invention, the rectangular tubes are assembled of two U-shaped half-shells whose bottoms are provided with projections pressed to shape. This construction of the rectangular tubes permits economical manufacture.
In a further embodiment of the invention, the projections have an oval base whose largest dimension extends in the flow direction. Advantageously, it is further provided that the projections have an essentially semicylindrical cross-section transversely to the flow direction. Projections of this type are easy to form while they offer the advantage that a linear support is obtained on the respective adjacent rectangular tube.
In a further embodiment of the invention, the bottoms of the half shells are equipped with lugs which diverge in a V-shape in the flow direction. In this case, it is also expediently provided that the projections and the lugs are arranged successively in a regularly spaced manner. Expediently, the arrangement is made such that the projections of one half shell are arranged opposite lugs of the other half shell. This ensures that favorable flow conditions exist also inside the rectangular tubes, while the mounting of the projections does not interfere with the mounting of the lugs.
In a further development of the invention, the rectangular pipes are widened in a tulip shape and are gas-tightly connected with one another. This replaces a tube bottom which leads to a significant saving of weight and, in addition, to a simplified manufacture.
In order to produce the jacket in a simple fashion, the jacket is assembled of two preferably deep-drawn sheet metal shells which are profiled in the longitudinal direction of the tube bundle such that they follow the outer contour of the tube bundle at a distance corresponding to the height of the projections of the rectangular tubes. As a result, it is ensured that flow ducts exist also in the area of the exterior rectangular tubes of the tube bundle, which flow ducts essentially correspond to the cross-sections of the flow ducts between the remaining rectangular tubes.
In a further development of the invention, in the area of the ends of the tube bundle, the sheet metal shells each form a surrounding ring duct, in which case a coolant inlet is molded to one ring duct and a coolant outlet is molded to the other ring duct, and in which case the coolant inlet and the coolant outlet are preferably situated approximately diagonally opposite one another. The ring ducts provide a good distribution of the liquid coolant. If the coolant inlet and the coolant outlet are situated approximately diagonally opposite one another, coolant ducts of essentially the same length are obtained so that a uniform heat transfer is achieved in the whole area of the heat transfer device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.